1. Field of the Invention
The present invention relates to a measurement system for scattering of light.
The system, in accordance with the invention, can be used for measuring the backscattering of light in a vertical, horizontal or freely selectable direction. It can be used for measuring cloud heights, visibility in desired direction, stratifications and contamination layers in the atmosphere as well as for measuring all forms of rain or similar physical parameters that lend themselves to measurement by means of scattered light. The system is applicable in meteorology and environmental protection as well as in the improvement of traffic safety, especially in the air, on roads and seaways, in addition to other sectors having needs for the measurement of similar environmental parameter values.
2. Description of Background Art
Conventional measurement systems for scattered light comprise a separate transmitter and receiver, which are aligned along essentially separate optical axes. The state of prior art technology will be described below in detail with the help the attached drawings.
A basic disadvantage of the prior art technology is that the computation of distance dependence in the received signal requires several assumptions to be made on the character of single and multiple scattering.
In addition to this basic disadvantage, conventional measurement systems bear the following technical problems:
The measurement system comprises two separate optical systems, whereby two sets of tubes, lenses or mirrors, windows (for exit and re-entry of radiation) as well as control mechanisms are required.
The mechanical stability of optical adjustments has an immediate effect on the measurement sensitivity. Hence, a deviation in the parallel alignment of optical axes as a result of a mechanical distortion will immediately be reflected as a change in the overlap function of beams. This further necessitates a sturdy mechanical construction resulting in a voluminous use of construction materials.
Both the transmitter and receiver optics must be adjustable; in addition, the optical axes must be aligned parallel in two planes.
Inhomogeneity of transmitter emission pattern, which is typical in semiconductor lasers, may lead to significant changes in measurement sensitivity especially in the distance range of 300 . . . 500 m.
The quality of selected optical components must be matched. For instance, a wedge error in one of the external windows (exit or entry window) may cause a nonparallelism error in the alignment of optical axes.
The distance from the light transmitter, conventionally a semiconductor laser, to the receiver conventionally a photodiode, is determined by the displacement of the optical axes. Together with the massive mechanical constructions required to achieve the desired stability in this kind of an arrangement, substantial electromagnetic disturbance will be conducted from the laser electronics into the circuitry of the receiver photodiode.